1. Field of the Invention
Generally, the present invention relates to heat dissipation nanocoating for electronic devices. More specifically, the present invention relates to a chemically functionalized molecular fan thin film coating for use as a heat dissipation device.
2. Description of the Related Art
Heat dissipation is a problem many electronic devices have to resolve. For instance, in personal computers, notebook computers, and the like, overheated environments affect the performance and reliability of these electronic devices. Many machine malfunctions can be traced to heat-dissipating problems. Heat generated by electronic devices and other equipment should be dissipated to enable efficient operation and to prevent damage to components. In some applications, a heat exchanger or heat sink may be used to effectuate the dissipation of heat. Forced convection may also be employed to enhance the performance of the heat exchanger.
There are three common mechanisms by which an object can release heat energy: conduction, convection, and radiation. In conduction, the heat is transferred within a substance. The best way to draw heat away from a component is conduction, as is done in the regular heat-sink and fan arrangement. This works especially well in substances such as metal, where the particles (metal atoms with mobile or delocalized electron sea) are not rigidly held in place, and the hotter, rapidly oscillating metal atoms transfer energy to cooler, slowly oscillating metal atoms by colliding with them. In convection, a hot region of a gas or liquid moves away from the source of heat. The hot fluid is replaced by cool fluid, which is then heated. This cyclical method of cooling is the common way for a modern machine to disperse heat.
A conventional personal computer has heat sinks attached to help draw heat away from processors and other components by conduction. Thermal conductive transfer tape, thermal conductive bonding agent, or a thermal conductive rubber sheet, is generally used to join the heat sink and the electronic parts. Mechanical fans are positioned near these heat sinks to draw the warm air away from the heat sink by convection. A modem PC has several fans (usually two or three) for this purpose.
The most convenient way to draw heat away from a component is conduction, as is done in the regular heat-sink-and-fan arrangement. However, when the heat is to be transferred to the surroundings and away from the computer, conduction is not the best solution. Radiation, the emission of energy as photons, is the best and most efficient way to transfer heat energy. Conduction of heat away from the component to the surface of the molecular fan thin film coating is still necessary whether by a heat sink or by simply molecular fan thin film coating the component itself.
There are several problems with the prior art arrangements. One is that more space is required to add more fans, because as the computer components become more powerful, they tend to release more heat and require more circulation to cool. Eventually the number of fans in the computer becomes cumbersome. Because of this, when the heat is to be transferred to the surroundings and away from the computer, convection is not the best solution. Another problem is present in miniaturization. As components, and therefore the computers and machines themselves, get smaller and smaller they will have less room for fans while concentrating heat production into a smaller area. This will result in a small center for a great deal of heat, and will require more efficient cooling. Using the presently available systems, eventually machines would have fans as their largest components. Mechanical fans also create their own heat when they convert magnetic potential into kinetic energy. This amount of heat is small, and is almost immediately dispersed by the action of the fan itself. With many fans in a small area, however, this heat can actually cause an increase in temperature over time, reducing the rate of cooling of heat sinks and components. Improving thermal performance of electronic components is very challenging due to the increasing power density and decreasing module sizes. The design trade off between electrical and mechanical characteristics and the cost of manufacturing products requires innovative solutions to improve the thermal performance of devices.
The primary cooling path in portable electronics serves to provide a low resistance path from the heat source to the system card and to spread the heat in its respective conductive layers. Numerous design techniques are implemented to achieve optimal thermal performance. However, conventional heat removal paths do not provide a sufficient thermal solution for small, mobile devices. Heat builds up in a local area and it is difficult for a small device to effectively dissipate the heat. Therefore, the use of heat pipe cooling systems in the electronic industry has been considered.
The cooling of mobile electronic devices such as personal digital assistants (PDAs) and wearable computers, has been studied by using a heat storage unit filled with the phase change materials (PCM) of n-eicosane inside the device. Desirable characteristics of a solid-liquid PCM include high heat of fusion per volume, congruent melting and freezing characteristics, high thermal conductivity, minimal supercooling, and low thermal expansion. Selecting a PCM for use in electronic cooling requires knowledge of the range of expected temperatures (the melt temperature of the PCM must be high enough such that melting does not occur until needed). Unfortunately just knowing the desired phase transition temperature is not sufficient to select a PCM. There are hundred of materials that melt in a temperature range useful for electronic cooling. However, the list of candidates becomes much smaller when issues such as material compatibility, toxicity (including environmental unfriendliness), availability of thermal property data, and cost are considered.
For example, in a computer system, the mother board has a central processing unit (CPU) for processing data operation. The CPU generates heat during operation and results in increasing temperature. When the temperature reaches a certain level, the CPU overheats and becomes unstable or even breaks down. The CPU is the main heat source of a computer system. To reduce the operation temperature of the CPU, a common practice is to install a heat sink on the CPU and place a fan on the heat sink so that the heat generated from the CPU is transmitted to the heat sink and the fan generates air flow to dissipate heat accumulated in the heat sink. In recent years, to meet the increasing demand of high-speed data processing, the manufacturing and design of CPUs have greatly improved. With improved performance and faster speed, operating voltages and frequencies for CPUs have also increased. Typically, a heat sink is arranged in close contact with a heat generating electronic component. As the power density of such components increases, heat transfer from the heat generating component to the surrounding environment becomes more and more critical to the proper operation of the component. Heat generated by the component is transferred to the heat sink and then dissipated from the heat sink to the surrounding air. One type of heat sink includes a metallic core in the form of a base plate. Heat dissipating fins extend from the base plate to increase the surface area of the heat sink. Heat transferred from the component to the base plate is spread throughout the base plate and to the fins fixed to the base plate. To further facilitate the dissipation of heat from the electronic component, a fan can be used to circulate air about outer surfaces of the fins and the base of the heat sink. As a result, the CPU operation temperature becomes much higher. To meet certain heat-dissipating requirements, it is necessary to enhance the heat-dissipating performance of fans.
In a conventional fan, the fan consists of a rotor and a stator. The stator is disposed in a frame of the fan and telescoped outside a bearing tube. The rotor has a shaft and a plurality of blades. The blades may generate airflow flowing toward the heat source. There is a pair of bearings disposed in the bearing tube to couple with the shaft. When the fan has increased its operational efficiency, operation temperature of the fan also increases (when the fan is energized, permanent magnets in the fan are excited by the stator and the rotor is driven to rotate and generate heat resulting from friction between the bearing and the shaft). The fan operating in high temperature environments tends to have a lower durability. Furthermore, bearings are prone to be damaged when operation temperature exceeds a certain level. Damaged bearings impact fan operation and also create noise.
As mentioned above, heat pipes have been used to dissipate heat. The heat pipe comprises a round shaped heat pipe and a flat shaped heat pipe. The flat heat pipe is favorably applied for cooling a component of an electronic device such as a CPU, or the like due to the fact that the heat pipe can be easily attached to the component to be cooled, and the heat pipe has a large contact area.
Furthermore, the heat pipe is classified by the manner in which it is attached to the component. The classes are: a top-heat mode heat pipe in which a heat absorbing side of the heat pipe is positioned above a heat dissipating side thereof; and a bottom-heat mode heat type in which the heat absorbing side of the heat pipe is positioned below the heat dissipating side thereof. In the bottom-heat mode heat pipe, a working fluid circulates via gravity. However, in the top-heat mode heat pipe, the working fluid has to be circulated against gravity, thus a capillary phenomenon of a wick is usually introduced in the heat pipe.
The heat pipe includes a hollow space that is prepared within the heat pipe which functions as a passage for working fluid. Heat is transferred by a phase transition between vaporization and condensation as well as movement of the working fluid. The heat pipe has a sealed hollow portion in which the working fluid is phase-transited and moved so as to transfer heat is operated as follows: In the heat absorbing side of the heat pipe, the heat generated by the component to be cooled and conducted through the material forming the container of the heat pipe is absorbed to vaporize the working fluid. The vaporized working fluid is transferred to the heat dissipating side of the heat pipe. In the heat dissipating side of the heat pipe, the vaporized working fluid is condensed to release the latent heat and returned to a fluid phase working fluid. The working fluid returned to a fluid phase circulates back to the heat absorbing side. Thus, the heat is transferred by the phase transition and movement of the working fluid.
In a gravity-type heat pipe, the working fluid returned to a liquid state by the phase transition moves (i.e., circulates) to the heat absorbing side of the heat pipe by gravity. In the top-heat mode heat pipe, the working fluid has to be circulated against gravity, thus a capillary phenomenon of a wick is usually introduced in the heat pipe.
Since a semiconductor device processing high speed signal generates a larger amount of heat, the above-mentioned heat pipe does not fully cool the device. In order to cool the semiconductor device generating large amount of heat, a cooling device in which a thermoelectric cooler, such as a Peltier device, is directly attached to the semiconductor device.
In general, when two kinds of conductors A, B are connected, and a current flows at a constant temperature, the heat is generated or absorbed at a contact point of the conductors A and B, which is known as the Peltier effect. More specifically, p-type thermoelectric semiconductor elements and n-type thermoelectric semiconductor elements are arranged alternately in parallel, and electrodes are placed at both ends of each of the semiconductor elements. Both ends of the respective semiconductor elements and the electrodes are jointed by soldering. Each of the p-type semiconductor elements and the n-type semiconductor elements, which are arranged alternately in parallel, are electrically connected in series through the corresponding electrodes.
An electric circuit which is formed by the electrodes, the p-type semiconductor elements, and the n-type semiconductor elements are electrically insulated from the outside by a pair of electrically insulated substrates which are arranged outside of the respective electrodes. The electrodes and the electrically insulated substrates are jointed by soldering. Thus, the Peltier device has a construction in which the electric circuit formed by the electrodes, the p-type semiconductor elements, and the n-type semiconductor elements are sandwiched by two electrically insulated substrates. By the above-described Peltier device, the heat at one of the electrically insulated substrates is transferred to the other electrically insulated substrate so that the one electrically insulated substrate side is cooled.
Conventionally, for example, as disclosed in Japanese Patent Provisional Publication No. 2004-071969, it is known that the heat from the heat generating source is spread by a heat receiving-spreading device, and the low temperature side of the Peltier device is attached to the heat receiving-spreading device, thus the heat is moved into the Peltier device. A copper heat sink is attached to the high temperature side of the Peltier device.
There are a number of problems in the conventional method in which the lower temperature side of the Peltier device is attached to the heat generating source while the higher temperature side of the Peltier device is attached to the heat sink. When the heat from the heat generating source (for example, CPU) increases, the heat absorbing of the Peltier device (TEC) is not sufficient, such that the thermal resistance of the cooling module rises. More specifically, it becomes difficult to enlarge the temperature difference between the heat sink and the cooling air, resulting in the deterioration of the cooling efficiency. For example, although the required temperature difference for the heat generating source of 120 W is 15 degrees centigrade, the temperature difference obtained by the easily available Peltier device is less than 12 degrees centigrade. It becomes difficult to sufficiently cool the heat generating source by the thermoelectric device, when the heat from the CPU is over 120 W under the condition of a spreading resistance of 0.10 K/W in the heat receiving-spreading device.
In addition, it is generally known that each component of the conventional cooling device is thermally connected by the use of a thermal grease. However, it is difficult to control the thickness of the thermal grease, leading to a large variation of the contact resistance between components. When the thickness of the grease is large, the total thermal resistance of the cooling module becomes high.
Alternatively, the performance and reliability of some electronic devices, such as high power CMOS circuits, can be improved using liquid cooling means such as refrigeration or water rather than air cooling. Non-redundant liquid cooling may help the circuits but the cooling system failure rate is too high for most electronics applications (e.g., servers) without a cooling backup.
Furthermore, the aggregated components of electronic devices may occupy considerable volumes within their respective systems such that redundant liquid cooling is not possible. Because space is at a premium in most electronics applications, particularly as the size of the systems is reduced to keep pace with technological trends, cooling systems may be likewise reduced in size. In addition, higher end modules having increased density of electronic circuitry require redundant or backup cooling means in the event that the primary refrigeration cooling unit fails, but it is often necessary to limit the space needed to employ such a redundant or secondary cooling means.
Finally, the amount of heat that can be dissipated may increase with the size and/or surface area of the heat exchanger. Where space constraints limit the size of a heat exchanger, the efficiency of the heat exchanger may become important. Some devices, for example, might be limited in speed or functionality because higher power components would generate more heat than could be effectively dissipated by a heat exchanger of a given size. It would therefore be beneficial to develop a device that can dissipate heat in electronic devices without increasing the size of the device.